Current discontinuity device



- Jan. 23, 1968 I INVENTOR. BURT J. B|TTNER Jan. 23, 1968 Y B. J.BITTNER 3,365,721

CURRENT DISCONTINUITY DEVICE Original Filed Oct. 11, 1965 Sheet-Sneel 6M 7 M I 2m: m if I 64 If 13 A/Z v l 56 V INVENTOR.

60 BURT J. BITTNER ATTORNEYS Jan. 23, 1968 J. rr 3,365,721

CURRENT DISCONTINUITY DEVICE Or ginal Filed 001:. 11, 1963 3Sheets-Sheet Z 6 pa, 2 f 76. 9.

96 92 96 0 g /mo x 1, 4 90a 7 v INVENTOR BURT- J. BITTNER H6. 13. BY

ATTORNEYS United States Patent Ofifice Patented Jan. 23, 1968 3,365,721CURRENT DISCONTINUITY DEVICE Burt J. Bittner, Black Forest, (3010.,assignor to Kaman Aircraft Corporation, Bloomfield, Conn, a corporationof Connecticut Continuation of application Ser. No. 315,573, Oct. 11,1963. This application Apr. 1, 1966, Ser. No. 539,585

13 Claims. (Cl. 343856) This is a continuation of application Ser. No.315,573, filed Oct. 11, 1963, now abandoned.

This invention relates to a new class of electrical components whichimpede the current flow in a conductor and which may be identified ascurrent discontinuity devices.

In this age of missiles and satellites and the attendant need foreffective communication between ground and remote stations and betweenseveral remote stations, good and efiicient antennas are required.Further, the use of an existing portion of a remote station as anantenna would be instrumental in reducing the weight of the station. Itis also important to minimize the interruption of streamlining andstrength of a structure to which an electromagnetic signal is applied orcoupled. To provide an effective antenna, for example, on thestreamlined surface of a missile creates a problem either in disruptingthe streamlining or weakening of the structural configuration. Oneapproach suggests the excitation of only a part of the missile, however,with the present state of the art, this requires that the excitedportion be electrically isolated from the balance of the structure orthat a slot antenna be used. Either of these solutions requires that thestructure be physically interrupted and weakened.

The device of this invention provides a novel means of the coupling ofelectromagnetic energy to and from transmission lines, antenna elementsand large structures which conveniently cannot physically be altered toprovide an electrical discontinuity.

It is an object of the present invention to provide a currentdiscontinuity device which overcomes certain disadvantages of prior artdevices.

It is a further important object of the present invention to provide acurrent discontinuity device which may be applied to an cXistingstructure without disrupting the electrical continuity thereof.

Another important object of the present invention is to provide a meansfor coupling to a portion of a structure of significant size withoutstructurally or electrically isolating a portion of the structure.

Another object of the present invention is to provide a currentdiscontinuity device having broad band characteristics.

A still further object of the present invention is to provide means forproducing broad band arrays which are tunable without disrupting theelectrical continuity thereof.

Another and further object of the present invention is to provide acurrent discontinuity device which is simple of construction,inexpensive to manufacture and effective in operation.

For a better understanding of the present invention, together with otherand further objects thereof, reference is had to the followingdescription taken in connection with the accompanying drawing and itsscope will be pointed out in the appended claims.

In the drawings:

FIGURE 1 illustrates a basic form of the invention;

FIGURE 2 illustrates a counterwound configuration of the invention;

FIGURE 3 illustrates a further embodiment of the invention wherein aseries of turns are parallel to provide a desired characteristic;

FIGURE 4 shows the invention as applied to a large structure;

FIGURES 5B and 5C are representations of radiation patterns of theantenna array of FIGURE 5A, FIGURE 5B being the pattern obtained withoutand FIGURE 5C being the pattern obtained with the current discontinuitydevice of this invention;

FIGURE 6 illustrates the use of the current discontinunity devices ofthe present invention to produce a tuned array from a long conductor;

FIGURES 7 and 8 illustrate an embodiment of the current discontinuitydevice of the present invention for coupling a coaxial cable to a waveguide;

FIGURE 9 illustrates the use of the present invention to coupleelectromagnetic energy to a multi-pedestal antenna;

FIGURE 10 illustrates the use of a plurality of devices according to thepresent invention to provide a multiple frequency capability;

FIGURE 11 illustrates another embodiment of the present invention toprovide impedance matching between circuits;

FIGURE 12 illustrates another form which the invention may take whereinthe coils are shielded; and,

FIGURE 13 represents a plot of admittance of a specific device accordingto the invention.

Referring now to the drawings, and in particular to FIGURE 1, thecurrent discontinuity device 10 of the present invention in its simplestform is comprised of a plurality of formed coupling loops 12 of anelectric conductor, series connected and a portion of which lies inclose parallel relation to a transmission line or conductor 14 toprovide a high order of coupling between the coil and the transmissionline. The loops in the device of FIG- URE 1 are formed in the shape of atoroid and the loops are preferably resonant at operating frequencies.The current discontinuity device is open'ended to direct current flowand may be self-resonating or may include a circuit element such ascapacitor 16 connected to terminals 18 and 20 to achieve resonance. Thevalue of the capacitor and the number of turns will vary depending uponthe frequency, the desired coupling coefficient and the distributedcapacity between the turns. The device acts to impede the current flowat resonance by the magnetostatic force on a moving charge due to theclosely coupled electrons in the associated loops. For greatest couplingefiiciency on the order of at least a portion of each loop should lie inclose parallel spaced relation to the conductor of not more than about0.005 of the operating wavelength. The parallel portion may be smallcompared to the frequency wavelength to be coupled and the length of thecoil should be small when compared to the wavelength or multiplesthereof.

As an active coupling device, a high impedance feed at resonantfrequency is available across terminals 18 and 20. A low impedance feedat resonant frequency is available by tapping down on the loops as byhaving the terminals across fewer turns. The basic uses of theconfiguration of FIGURE 1 are as a wave trap on an antenna structure andas a band-reject filter in a coaxial line. The center conductor is thusseen to be structurally undisturbed and yet provides 90% and betterefiective coupling and enclosing of the magnetic field.

Where it is desirable to couple to a conductor of such a size that thetotal length of coupling elements required to surround the conductorbeing to approach self-resonance, a parallel connected counter-Woundconfiguration of the coupling loops may be used as in FIGURE 2. Here,the conductors 22 forming the loops may be fiat ribbon wound on aninsulating coil form 24 which may be of plastic and the like. The coil26 is made up of two counterwound sections 26a and 261; being connectedin parallel 3 as at terminals 28 and 3t and the length of each sectionis not greater than that providing self-resonance at the operatingfrequency. A capacitor 16 may be connected across terminals 28 and 30for tuning purposes. This configuration provides maximum separation ofthe feed terminals which is desirable in some high power applications.

Thus, it is seen that the current discontinuity device may be usedaround a structure of considerable size by paralleling many coilsections each of a length not greater than that providing self-resonanceat the operating frequency. An embodiment of this arrangement is shownin FIG- URES 3 and 4. By paralleling many sections, a structure, such asa missile 34, with a circumference or dimension greater than awavelength can be properly excited. In this case, as in the applicationto smaller structures, the current discontinuity device is a means forfeeding the structure as well as being a means of providing aparasitically excited system.

With particular reference to FIGURE 3, it has been discovered that thesurface to be excited need not be a figure of revolution and thus alinear section of a missile or aircraft 34 can be excited by a fiat coilarrangement 36 arranged about an insulating form 38. Each coil 36a, 36b,36c and 36d is connected in parallel with the other and the coils areinsulated from the missile 34 as by a layer of insulation. The coils 36are connected to a generator (not shown) via conductors 40 and 42connected respectively to the ends of the coils. While the length of thecoil arrangement 36 is preferably a half-wavelength at the operatingfrequency for greatest efiiciency, the length can be less than ahalf-wavelength or several wavelengths in length so long as theindividual coils 36a, 36b, 36c, etc., are each effectivehalf-wavelengths at the operating frequency. For greatest couplingetficiency, a plurality of coil arrangements of FIGURE 3 sufficient toencircle or extend the length of the body to be driven and dimensionedor tuned to a half-wavelength of the operating frequency would beconnected in series-parallel.

The missile 34 of FIGURE 4 is provided with an annular recess 44 withinwhich is positioned a plurality of coils 46 connected in parallel, as inFIGURE 3, to be driven in phase, to excite a portion of the missilewithout the necessity of structurally or electrically isolating samefrom the balance of the missile structure. The coils 46 are electricallyinsulated from the missile. The annular recess 44 and flap 48 define anelectrostatic shield around the coil and serve to protect the structureand provide effective coupling to the missile. The flap 48 extends fromone side of the annular recess to just short of the other side to definecover having a gap or split 50 along one edge. Split 50 may be filledwith an insulator 52.to maintain the streamlined profile. The coils 46comprise a plurality of parallel connected coils much in the manner ofthe coils 36 in FIGURE 3. The missile structure 34 is capable of thusbeing excited by an isolated small feed at current points. The provisionof a shield produces close coupling between the current discontinuitydevice and the structure being driven. Through the use of a split shielda reduction in the size of coil can be made while maintaining asufficient degree of coupling. The current discontinuity deviceeffectively isolates one portion of the missile from another forpurposes of its use as an antenna. Similarly, portions of aircraft,buildings and even mountains and islands can be energized, actively orpassively, as an antenna.

Referring to FIGURE 5, there is represented radiation patterns of anantenna array 54, FIGURE 5A, about which a passive current discontinuitydevice 56 is positioned. Device 56 consists of a toroid coil 58 having avariable capacitor 60 connected thereacross. The patterns of FIGURE 5Brepresents that obtained from antenna 54 less the current discontinuitydevice 56 or with same detuned from resonance at the frequency beingtransmitted. FIGURE 5B shows a pattern with multiple lobes and islacking in controlled directivity. n the other hand, the pattern ofFIGURE C represents the radiation obtained from antenna 54 wherein thecurrent discontinuity device is in place and tuned to resonance with thefrequency being transmitted. The pattern obtained is essentially thefamiliar and desired FIGURE 8 pattern which provides directivity andgain in a desired direction. It is to be noted that the device of thepresent invention functions as a Wave trap when placed at a desiredcurrent maximum as opposed to parallel resonant wave traps which must beplaced at a voltage maximum and in the line or antenna The presentdevices are also seen to differ from the parallel resonant wave trap inthat at frequencies off-resonance it does not disturb the transmissionline measurably and further can be repositioned by being slid along theline to a desired point.

FIGURE 6 illustrates another embodiment wherein the currentdiscontinuity devices according to the present invention are utilized inboth active 62 and passive 64 forms. The devices are positioned alongthe length of a long wire 66 to provide an array tuner. The activedevice 62 is positioned centrally of wire 66 and a plurality of passivedevices 64 are positioned along the length of the wire at points wherecurrent discontinuity is desired usually spaced as a function of thewave length of the frequencies being fed to the array. The dotted lines68 represent the plot of voltage (standing wave) along the line. Thedevices of this invention are installed over the wire and avoidphysically breaking into the wire as is required in following knownpractices where Wave traps are inserted in the wire and are structurallydifiicult and expensive to use.

FIGURES 7 and 8 illustrate the use of the device of this invention toprovide a coupling between a coaxial cable 70 and a wave guide 72. Itwill be seen that the center conductor 74 of the coaxial cable isconnected to one end of coil 76, the other end of which is connected tothe wave guide 72. The shield 78 of the coaxial cable is also connectedto wave guide 72. The coil 76 is preferably wound about an insulatedform 80 in the same manner as that of coil 36 in FIGURE 3 and the coilmaybe counter-wound as in FIGURE 2.

FIGURE 9 shows an antenna tower 82 with parts broken away to conservespace, with a current discontinuity device 84a, 84b and 840 about eachleg. The devices 84a, 84b and 84c are connected in parallel and drivenin phase to effectively provide isolation from ground and avoid thenecessity of the use of heavy insulators. This arrangement furtherpermits tower 82 to be grounded directly for lightning protection. Thedevices 84a, b and 0 should be resonant at the transmission frequencyand multiple units would be used where more than one frequency isencountered.

An alternate feed arrangement may be utilized where devices 84a, b and care passive, parasitically excited and the energy is coupled to antennatower 82 above the positioning of devices 84a, b and c.

FIGURE 10 illustrates an antenna 86 with portion broken away to conservespace, on which is positioned a driven current discontinuity device 88and a plurality of.

passive devices 90a, b, c, d, e and f to provide a broad tuned array.Device 88 is chosen to be resonant at a se lected frequency within thespectrum of frequencies to be transmitted or received by the antenna 86.The passive devices 90a, b, c, d, e and f are positioned immediatelyadjacent each other along the antenna and are mutually coupled. Devices98a, b, c, d, e and f are each chosen to be resonant at a differentfrequency. The paratisitic devices 9011, b, c, d, e and f are spacedfrom driven device 88 by an even fraction of a wavelength of thefrequency at which they resonate, such as a half wavelength. Theproximity of the devices provides a coupling from one device to the nextuntil the particular device resonant at the desired frequency isreached. This arrangement provides an antenna which is efiicient in usewith multiple frequencies encompassing a considerable bandwith.

FIGURE 11 shows a device of the invention as used in an impedancematching device in the nature of a balun coil to match a low impedanceline, such as a co-axial cable 92 with a high impedance. The centerconductor 94 of the cable is intact throughout its length and has aportion extending beyond the shield 96. A toroidal coil 98 is shownpositioned around the unshielded center conductor 94 with one endthereof being connected to the shield 96. The other end of coil 98 alongwith the unshielded center conductor comprise the high impedanceterminals 100 of the device. The coil 98 can also be successfullypositioned about the outer shield.

FIGURE 12 illustrates another embodiment of the invention for use as adirectional coupling with parts broken away to conserve space. Thetoroidal coil 102 is positioned externally of a large diameter antenna104. The coils are surrounded by a split shield 106. The split 108between one margin of shield 106 and antenna 104 may be filled with aninsulator material for weatherproofing purposes. The ends of coil 102are each connected to center conductor 200 and 202 of coaxial cables 204and 206 which may be connected together through an irnpedance, such as atuned capacitor, and associated active circuitry, such as vacuum tubeamplifiers and varactors, or the cables may be fed to independentcircuits. Electromagnetic energy from the direction of the arrow 208will produce signals between the center conductors and outer shields ofa different phase and magnitude that signals from a direction oppositefrom the direction of arrow 208, thus permit either directionaltransmission or a determination of the direction of a recovered signalas a function of the phase and magnitude of the signals available acrosscables 204 and 206.

FIGURE 13 represents the plot of admittance of a specific tunablecurrent discontinuity band reject, band pass filter design tested in an\NBS tracking station having coil portions parallel with the conductorfor a distance as small as 0.1 of the wavelength and being spacedtherefrom on the order of .0002 wavelength to provide couplingsubstantially in excess of 90% on the order of 99.9%. The circuitconfiguration is essentially that of FIGURE 1 utilizing a multiplegrouping in series parallel. As a simple band reject filter, it wasmatched (VSWR 1.1) from DC through 115 me. and from 113 me. through toover 300 me. The reject notch was tunable from 5 mc. to 256 me. and wasset at 121 me. for these tests. The theoretical analysis of the devicesindicate that there are no transcendental, or harmonically relatedspurious response characteristics of significance.

While there have been described what at present are considered to be thepreferred embodiments of this invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein without departing from the invention and it is to be understoodthat all matter herein is to be interpreted as being illustrative andnot by way of limitation. It is aimed, therefore, in the appended claimsto cover all such changes and modifications which fall within the truespirit and scope of the invention.

What is claimed is:

1. A current discontinuity device comprising in combination, anelongated multiple loop D.C. open-ended coil of a conductor having alineal length providing an effective electrical half-wavelength at thefrequency with which it is to be used, said coil having a non-magneticcore and another electrical conductor electrically isolated from saidcoil wherein a substantial portion of each loop of the coil lies in suchclose coupled parallel relation to the other conductor and in suchimmediate proximity to other conductor for substantial distance which issmall compared to the Wavelength of the frequency with which it is to beused as to provide coupling on the order of at least 90% between saidcoil and said other conductor.

2. The current discontinuity device according to claim 1 wherein themultiple loop coil is of toroidal configuration completely surrounding aconductor in close coupled relation.

3. A current discontinuity device which comprises a plurality ofmultiple loop coils of claim 1 connected in series-parallel relation.

4. A current discontinuity device comprising in combination, a multipleloop coil having a non-magnetic core connected in series with acapacitor and a conductor electrically isolated from said coil wherein aportion of each loop lies in close parallel relation to the conductorand includes an electrostatic split-shield surrounding the coil withsaid shield being in electrical continuity with the conductor 5. Acurrent discontinuity device according to claim 4 wherein the coilincludes a plurality of multiple loops connected in series-parallelrelation and the conductor is of planar configuration.

6. A current discontinuity device according to claim 4 wherein the coilincludes a plurality of multiple loops formed in a toroidalconfiguration concentric with the conductor, said loops being connectedin series-parallel relation and the conductor is of circularcross-section.

7. A current discontinuity device comprising in combination, a pluralityof elongated multiple loop coils each of toroidal configuration having anon-magnetic core, a capacitor in series with each coil, each coil beingformed of a conductor having a lineal length providing an effectiveelectrical half-wavelength at the operating frequency and anotherconductor electrically isolated from said coils wherein the coils aremounted in concentric relation about the other conductor in spacedrelation along the length thereof at positions where currentdiscontinuity is desired and wherein a portion of each loop of a coillies in such close parallel relation to the other conductor for asubstantial distance which is small compared to the Wavelength of theoperating frequency as to provide coupling on the order of at leastbetween said coils and said other conductor.

8. A current discontinuity device in accordance with claim 7 whereineach coil and capacitor pair resonate at progressively differentfrequencies.

9. A current discontinuity device comprising in combination, a pluralityof elongated multiple loop coils of toroidal configuration having anon-magnetic core, each coil connected in series with a capacitor and inparallel with each other, each coil being formed of a conductor having alineal length providing an effective half-wavelength at the operatingfrequency and another conductor electrically isolated from said coils,at least a portion of said other conductor enclosed in concentricrelation by a coil and wherein a portion of each loop of a coil lies insuch close parallel relation to the other conductor for a substantialdistance which is small compared to the wavelength of the operatingfrequency as to provide coupling between said coils and said otherconductor on the order of at least 90%.

10. A current discontinuity device according to claim 9 wherein eachcoil is enclosed by an electrostatic split shield which is in electricalcontinuity with the other conductor enclosed by said coils.

11. A current discontinuity device comprising in combination, anelongated multiple loop D.C. open-ended coil having a non-magnetic coreand an electrical conductor electrically isolated from said coil whereina portion of each loop lies in close parallel relation and in immediateproximity to the conductor for a substantial distance which is smallcompared to the wave length of the frequency with which it is be used,the length of the coil is small when compared to such wave length andwherein the device includes an electrostatic split-shield surroundingthe coil with the shield being in electrical continuity with theconductor and a device is positioned along the conductor where a currentdiscontinuity is desired.

12. A current discontinuity device comprising in combination, anelongated multiple loop coil with a non-magnetic core, said coil beingconnected in series with a capacitor to provide an effective electricalhalf-wavelength at the operating frequency and a conductor electricallyisolated from said coil wherein a portion of each loop lies in closespaced parallel relation to said conductor wherein the spacing betweensaid portion of each loop and said conductor is selected to provideelectrical coupling of at least 90% therebetween and the total length ofthe coil is small compared to a whole wavelength.

13. In an antenna connected to ground potential, a current discontinuitydevice positioned intermediate ground potential and a drive connectionthereto, which device comprises an elongated multiple loop D.C.openended coil of a conductor having a lineal length providing aneffective electrical half-wavelength at the frequency to be usedtherewith, said coil having a non-magnetic core and being electricallyisolated from said antenna and wherein a substantial portion of eachloop of the coil lies in such close coupled parallel relation to theantenna and in such immediate proximity thereto for a substantialdistance which is small compared to the wavelength of the operatingfrequency so as to provide electrical coupling between said coil andsaid conductor on the order of at least 90%.

References Cited UNITED STATES PATENTS 2,159,648 5/1939 Alford 333 732,283,670 5/1942 Evans 336-174 2,296,356 9/1942 Lindenblad 3361742,527,609 10/1950 Willoughby 333 77 2,611,080 9/1952 Brough 3 3 18FOREIGN PATENTS 338,982 12/1930 Great Britain.

HERMAN KARL SAALBACH, Primary Examiner.

R. F. HlUNT, M. NUSSBAUM, Assistant Examiners.

13. IN AN ANTENNA CONNECTED TO GROUP POTENTIAL, A CURRENT DISCONTINUITYDEVICE POSITIONED INTERMEDIATE GROUND POTENTIAL AND A DRIVE CONNECTIONTHERETO, WHICH DEVICE COMPRISES AN ELONGATED MULTIPLE LOOP D.C.OPENENDED COIL OF A CONDUCTOR HAVING A LINEAL LENGTH PROVIDING ANEFFECTIVE ELECTRICAL HALF-WAVELENGTH AT THE FREQUENCY TO BE USEDTHEREWITH, SAID COIL HAVING A NON-MAGNETIC CORE AND BEING ELECTRICALLYISOLATED FROM SAID ANTENNA AND WHEREIN A SUBSTANTIAL PORTION OF EACHLOOP OF THE COIL LIES IN SUCH CLOSE COUPLED PARALLEL RELATON TO THEANTENNA AND IN SUCH IMMEDIATE PROXIMITY THERETO FOR A SUBSTANTIALDISTANCE WHICH IS SMALL COMPARED TO THE WAVELENGTH OF THE OPERATINGFREQUENCY SO AS TO PROVIDE ELECTRICAL COUPLING BETWEEN SAID COIL ANDSAID CONDUCTOR ON THE ORDER OF LEAST 90%.